This invention relates to welding apparati or installations, and more particularly to a new contact tip made of copper and carbon wherethrough a continuous metal wire electrode is passed through and charged to create the filler metal on the work piece.
In welding methods of this general category, the filler metal or metal wire is unwound from a reel and is automatically regulated or fed into the welding assembly as the filler metal is consumed. The filler metal wire has a cast, which is arcuate in nature, as it is formed and wound on the reel and is desirable to maintain good electrical continuity between the wire and the contact tip. Drive rollers are often used to feed the wire off the reel and into the welding mechanism. The wire must be moved along the weld line smoothly and without jerking for accurate and high performance welding to be satisfactorily achieved.
Traditionally, the wire of filler metal is guided by a copper tube or contact tip having a bore with a rear opening through which the wire enters the contact tip and front opening through which a short length of the wire projects to be presented in a suitable position next to the weld zone. In many methods and apparati, a welding machine further includes a nozzle for blowing an inert or active gas over the weld zone to keep it under a controlled atmosphere. This avoids unwanted reactions of the molten filler metal and work piece material with the surrounding air or possibly with the gases evolved by the welding operation.
In high performance welding machines, the position relative to the weld of both the gas nozzle and of the system for feeding the filler wire to the weld zone are adjustable under the control of an automatic regulator apparatus which further may include drive rolls for moving the wire through the welding apparatus and along the weld line. The automatic regulator apparatus maintains certain parameters of welding operation beyond the filler metal feed to include the are current thereby optimizing operating conditions.
In high performance and accurate welding, efficiency in labor is measured by arc or actual welding time. Typical actual arc time may be forty to sixty percent of the laborer's time on the job. The time in which the laborer is not welding generally relates to the difficulty of use of the welding apparatus together with the deterioration of the metal contact tip or tube.
In particular, at the end of the filler metal wire after a breakaway from the last weld is located a ball or glob of filler metal. With the ball at the end of the wire and the welder ready to begin a new weld bead, the automatic regulator apparatus senses the need for a high power surge or amperage which is necessary to burn off the ball and to permit accurate and high performance welding. A high current surge at the beginning of the weld often causes burn back of the filler metal into the contact tip with resulting fusion of the wire and contact tip. Also, the current surge at the beginning of the weld can cause the contact tip to greatly heat up and possibly overheat. This is particularly true where the contact tube is also used to supply electricity to the filler metal as well as to guide the filler metal wire. Overheating of the contact tip causes tip expansion and contraction of the hole, tunnel or aperture therethrough, thereby restricting or causing friction or resistance in the feeding of the wire through the tip. This will affect the drive rolls on the wire and cause skidding which in turn causes flat spots on the wire which may further affect and fluctuate the arc length.
Also occurring within the aperture of the contact tip is wear caused by friction due to the cast of the wire and by flat or uneven surfaces in the wire itself. This creates elongation and unevenness in the aperture through the contact tip which in turn also causes parasitic electric arcs within the tip itself. This affects the welding performance as well as the beginning of deterioration of the contact tip by way of oxidation, overheating, reduced continuity between the metal filler wire and contact tip, and increased amperage and creation of micropores inside the tunnel or aperture of the tip. In this situation, the welding apparatus may begin to operate erratically, affecting the arc length, and the tip of the filler metal wire may actually burn back and weld itself within the contact tube and the automatic regulation mechanism ceases to operate correctly, effectively and completely shutting down the welding apparatus or assembly. A shut down of the welding apparatus is commonly associated with some problems in the feeding or drive rolls which may have skidded on the filler metal wire causing flat spots which must be dealt with once the welding assembly is again operational. These difficulties lead to the contact tip or guide tubes needing to be replaced frequently which is an expensive operation since it halts production and constitutes a large amount of labor time and further consumes a large number of contact tips. Additionally, weld quality is adversely affected when the filler metal drive mechanism becomes erratic due to drive roll skidding.
Attempts have been made to improve the electric contact between the wire filler metal and the contact tip such as with biased ball bearings within the contact tip or placing a protective refractory material over the end and side walls of the contact tip where the filler metal wire exits the tip acting as an insulator with no electrical continuity close to the welding arc where it is most efficient. Further, these mechanisms are too complex and do not stand up well to the very high operating temperatures of the contact tubes.
There is a need for an improved contact tip that provides for good continuity with a smoother, more even are due to contact tip tunnel or aperture lubricity as associated with carbon, and reduced coefficient of expansion. Such a tip should have a longer tip life, cooler operation and thus a longer arc time for the laborer. Such a tip should have high electrical conductivity with low thermal conductivity, a high melting point and an excellent thermal shock resistance and improved lubricity. Such a tip may be easily manufactured by injection molding or simple machining to reduce costs.